Handover method in mobile communication system

ABSTRACT

In a mobile communication system having an ATM-processed transfer path, a non-instantaneous interrupt handover can be realized. In a mobile communication network including an ATM-processed transfer path, when a mobile station is moved between cells during communication, frames are received to be identified by a mobile switching center. The frames contain the same data received from both base stations covering the cell range at asynchronous timing different from each other. A selection is made of header information with the lowest error rate from the header information of these frames. The frames are connected at instructed timing. Also, the frames to be transmitted to a plurality of base stations are duplicated, and then transmission timing is specified from these header information. These duplicated frames are transmitted at the specified transmission timing, so that the non-instantaneous interrupt handover is carried out.

BACKGROUND OF THE INVENTION

[0001] The present invention is related to a non-instantaneous interrupthandover method and an apparatus capable of realizing such anon-instantaneous interrupt handover in a mobile communication system.

[0002] In mobile communication systems with using the CDMA (codedivision multiple access) system, non-instantaneous handover isrealized. For instance, wireless (radio) interfaces are defined basedupon the EIA/TIA/IS-95 standard as the portable telephone standardsystem in USA. Similarly, this EIA/TIA/IS-634 defines interfaces betweenbase stations and a mobile switching center.

[0003] In these mobile communication systems, the soft handoff or softhandover techniques have been employed as the service area switchingtechniques during communications. In this soft handover technique, aplurality of communication paths are set at the same time between mobilestations and a mobile switching center, and the same communication datais transmitted/received via a plurality of these communication paths.Data having a low error rate is selected, or the same communication datais synthesized with each other on the reception side, so that the datacommunication with the low error rate is performed. As a consequence,when the channels are switched during the handover, no discontinuity isproduced in the channel under use. Thus, no data drops out, and thehandover can be realized without any instantaneous interrupt.

[0004] However, the above-described prior art technique owns such aninitial condition that the data transfer operation in the mobilecommunication system is carried out in the STM system (synchronoustransfer system). For instance, when the synchronization of the framescontaining the respective data is maintained in the transfer pathbetween the base stations and the mobile switching center, the framesare transmitted/received only in the specific timing. As a result, thecontrol unit of the mobile switching center merely makes up therelationship between the specific slot and the connection in thetransfer path, but need not especially perform the synchronizations inunit of slot and frame during the transmission/reception operations. Asa result, even the soft handover is initiated, the data of therespective slots received at the same time, or the specific timingdifferent from each other can be compared with each other and can beselected. Even when the same data is transmitted to each of the pluralbase stations, if the same data are duplicated and the duplicated dataare transmitted by way of the slots for the handover, than the data ofthe corresponding slot are synthesized, and selected on the side of thebase station, or the mobile stations. Thus, the non-instantaneoushandover (soft handover) can be readily realized.

[0005] On the other hand, one proposal has been made so as to increasethe line utilization efficiency by using ATM (asynchronoustransfer)-processing having the above-described transfer path and totransfer each of the above-described data by using the ATM cells.

[0006] Even when this asynchronous system is employed in the transferpath, there is a first problem that the continuity of the informationduring the handover must be maintained.

[0007] Also, when the above-described transfer path is ATM-processed, aspreviously described, the relationship between thetransmission/reception timing, the connection, and the channel cannot beexclusively specified.

[0008] There is a second problem. That is, in the mobile switchingcenter, either the cell or the frame should be identified which containsthe same data related to the same handover from a plurality of datareceived in the mutually different asynchronous timing from the basestations.

[0009] Also, there is a third problem. That is, the connection isspecified in unit of the cell, or the frame received from the basestation, and the judgement is made as to whether or not the handover isinitiated in connection therewith. These comparing process and selectingprocess must be sequentially carried out in unit of the cell, or theframe.

[0010] Furthermore, there is a fourth problem. That is, if the handoveris initiated, then either the cells or the frames to be transmitted tothe base station are duplicated. Thereafter, these duplicated cells orframes should be transmitted at the same time in such timing that thedelays and the flickers determined based on the negotiations with thebase stations are minimized.

SUMMARY OF THE INVENTION

[0011] An object of the present invention is to provide such a mobilecommunication system capable of realizing non-instantaneous interrupthandover even when a transfer path of an asynchronous system is presentbetween mobile stations and a mobile switching center such as theabove-described transfer path.

[0012] Further, another object of the present invention is to provide ameans for identifying either a cell or a frame containing the same datarelated to the same handover from a plurality of data received from basestations at mutually different asynchronous timing in the mobileswitching center in the above-described mobile communication systemwhile non-instantaneous interrupt handover is initiated.

[0013] Moreover, another object of the present invention is to provide ameans for comparing the respective error rates of the identified cellsor frames, for selecting such a cell or frame having the smallest errorrates, and for transmitting this cell or frame having the smallest errorrate at instructed timing.

[0014] A still further object of the present invention is to providesuch a means for duplicating data to be transmitted to the basestations, and for transmitting either the cells or the frames containingthe duplicated data at the same time in specific timing int he mobileswitching center in the above-described mobile communication systemwhile non-instantaneous interrupt handover is initiated.

[0015] To achieve the above-described objects, according to an aspect ofthe present invention, in a mobile communication system arranged by aplurality of mobile stations, a plurality of mobile stations, aplurality of base stations for storing therein these mobile stations,and a mobile switching center for storing therein these stations, eithera cell or a frame containing the same data related to the same handoveris identified based on header information thereof from a plurality ofdata received from the base stations at mutually different asynchronoustiming; error rates of the identified frames are compared with eachother to select the frame having the smallest error rate; this cell orframe having the smallest error rate is transmitted at instructedtiming; data which should be transmitted to the base stations areduplicated from information (header information) related to this data;and either cells or frames containing the duplicated data aretransmitted at the same time at such transmission timing specified fromthe header information thereof.

[0016] Also, according to another aspect of the present invention, ahandover method of a mobile communication system in a wirelesscommunication system constituted by a base station communicated with aplurality of wireless stations, and a mobile switching center connectedto a plurality of said base stations, is featured by comprising: a stepfor initiating a handover process operation in order that while any ofthe wireless stations is connected to a first base station, the anywireless station should be newly connected to a second base stationirrelevant to the first base station; a step such that the wirelessstation is newly connected to said second base station while keeping theconnection with said first base station by the wireless station; a stepsuch that the first and second base stations convert the transmissioninformation from the wireless station into an ATM cell and thentransmits the ATM cell to the mobile switching center; a step such thatthe mobile switching center receives a first ATM cell transmitted by thefirst base station and a second ATM cell transmitted by the second basestation; a step such that the first ATM cell and the second ATM cell,which are received at asynchronous timing, are synthesized with eachother; a step for calculating error rates of the first and second ATMcells synchronized with each other; a step for selecting such an ATMcell whose error rate is lower than that of the other ATM cell; and astep such that when such a condition that the error rate of the secondATM cell exceeds the error rate of the first ATM cell becomes a normalcondition, the connection between the wireless station and the firstbase station is cut out.

[0017] Also, according to the present invention, the step forsynchronizing the first ATM cell with the second ATM cell, which arereceived in the asynchronous timing, corresponds to a step fortemporarily storing the first and second ATM cells received in theasynchronous timing into a buffer so as to be synchronized with eachother.

[0018] Also, the handover method of the present invention is furthercomprised of a step for discarding the ATM cell having the higher errorrate.

[0019] According to another aspect of the present invention, acommunication method is featured by comprising: a step such that aplurality of the base stations separately receive informationtransmitted from the same mobile wireless station in a parallel manner;a step such that the base stations superimpose the received informationon an asynchronous frame and transfers the superimposed asynchronousframe to the information processing station; and a step such that whenthe information derived from the same mobile station is superimposed onthe asynchronous frame via the plurality of base stations and then theasynchronous frames are transferred, the information processing stationselects an asynchronous frame having a better condition from theasynchronous frames.

[0020] Also, according to another aspect of the present invention, acommunication method is featured by comprising: a step such that themobile station adds a frame transmission order to frames to betransmitted; a step such that a plurality of the base stationsseparately receive information transmitted from the same mobile wirelessstation in a parallel manner; a step such that the base stations convertthe received frame into an asynchronous frame and transfers theconverted asynchronous frame to the information processing station; anda step such that when the information derived from the same mobilestation is superimposed on the asynchronous frame via the plurality ofbase stations and then the asynchronous superimposed frames aretransferred, the information processing station selects an asynchronousframe having a better condition from the asynchronous superimposedframes to which the same transmission order has been added.

[0021] Also, according to the present invention, the same transmissionorder corresponds to a connection number specifically determined everytime a single communication is established.

[0022] Also, a communication method, according to another aspect of theinvention, is featured by comprising: a step such that the mobilestation adds to a frame, information for indicating whether or not ahandover process operation is initiated; a step such that a plurality ofthe base stations separately receive frames transmitted from the samemobile wireless stations in a parallel manner; a step such that the basestations convert the received frames into asynchronous frames and thentransfer the converted asynchronous frames to the information processingstation; a step for judging information for indicating whether or notthe handover process operation is under initiation, which is added tothe frame; and a step such that when the judgement result indicates thatthe handover process operation is under execution, the informationprocessing station causes the asynchronous frames transferred from thesame mobile station via the plurality of base stations to be stored intoa buffer, selects such an asynchronous frame having a better condition,and outputs the selected asynchronous frame, whereas when the judgementresult indicates that the handover process operation is not underexecution, the information processing station directly outputs thereceived asynchronous frame.

[0023] Further, a handover method of the invention is featured bycomprising: a step for initiating a handover process operation in orderthat while any of the wireless stations is connected to a first basestation, the any wireless station should be newly connected to a secondbase station irrelevant to the first base station; a step such that thewireless station is newly connected to the second base station whilekeeping the connection with the first base station by the wirelessstation; a step such that the mobile switching center duplicatesdown-stream information to the mobile wireless stations, the number ofwhich is equal to the number of the base stations for executing thehandover process operation; converts the duplicated down-streaminformation into ATM cells; and transmits the ATM cells to the first andsecond base stations equal to handover sources; a step such that thebase station receives the ATM cells transmitted from the mobileswitching center and then transmits the received ATM cells to the mobilewireless terminal; and a step for cutting out a connection with any oneof the base stations.

[0024] Moreover, according to the invention, the mobile switching centeris comprised of the steps of: recognizing whether or not a framecontaining data to be transmitted to the mobile wireless terminalsbelongs to a connection of any end-to-end; applying such a numberindicative of the same frame transmission order to a frame which isjudged as the same connection by the recognizing step; duplicating theframe to which the frame transmission order number has been applied toobtain a plurality of such frames whose number is equal to a totalnumber of the base stations which execute the handover processoperation; and synchronizing the duplicated frames with each other andtransmitting the synchronized duplicated frames.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] For a better understanding of the present invention, reference ismade of a detailed description to be read in conjunction with theaccompanying drawings, in which:

[0026]FIG. 1 illustratively shows an arrangement of a mobilecommunication system according to the present invention;

[0027]FIG. 2 is a schematic block diagram for representing an internalarrangement of a mobile switching center according to the presentinvention;

[0028]FIG. 3 is a schematic block diagram for indicating an arrangementof a non-instantaneous interrupt handover unit employed in the mobileswitching center according to the present invention;

[0029]FIG. 4 is a schematic block diagram for showing an arrangement ofa frame synchronizing/selecting unit employed in the non-instantaneoushandover unit according to the present invention;

[0030]FIG. 5 indicates a channel/connection management table employed inthe frame synchronizing/synthesizing unit according to the presentinvention;

[0031]FIG. 6 represents a synthesizing parameter table provided in theframe synchronizing/synthesizing unit according to the presentinvention;

[0032]FIG. 7 is a sequence diagram for representing a data frame andsignal transmission/reception executed in the framesynchronizing/synthesizing unit according to the present invention;

[0033]FIG. 8 is a schematic block diagram for showing an internalarrangement of a frame multicasting unit employed in thenon-instantaneous handover unit according to the present invention;

[0034]FIG. 9 is a sequence diagram for representing a data frame and asignal transmission/reception executed in the frame multicasting unitaccording to the present invention;

[0035]FIG. 10 is a diagram for showing a sequential operation of thenon-instantaneous interrupt handover according to the present invention;

[0036]FIG. 11 is a diagram for indicating a sequential operation ofconnection setting according to the present invention; and

[0037]FIG. 12 schematically shows a frame structure according to thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] Referring now to drawings, various embodiments of the presentinvention will be described.

[0039]FIG. 1 schematically illustrates an overall arrangement of amobile communication network system to which the present invention isapplied, and schematically represents such an idea thatnon-instantaneous interrupt handover is carried out by embodying thepresent invention in this mobile communication network. This networkstores a plurality of mobile stations (MSs) 100. Each of base stations(BSs) 200 is connected via a plurality of wireless (radio) lines 150 tothe mobile stations 100. A cell 220 is a range in which the respectivebase stations can communicate with the mobile stations 100 with keepingcommunication qualities higher than a preselected quality. A mobileswitching center (MSC) 300 stores a plurality of base stations 200 via aplurality of wire transfer paths 250. Also, the mobile switching center300 is connected via an upper-grade network connection line 900 to anupper-grade network.

[0040] Assuming now that a mobile station 100 is being moved near anarea boundary between a cell 220A and another cell 220B (mobile stationis moved from cell 220A to cell 220B), and also non-instantaneousinterrupt handover is initiated, the mobile station 100 will communicatevia the respective wireless lines 150A and 150B to the respective basestations 200A and 200B at the same time. Communication data and controldata transmitted from the mobile station 100, i.e., the same data aretransferred via different paths, i.e., a path of the wireless line150A-base station 200A-wire line 250A, and another path of the wirelessline 150B-base station 200B-wire line 250B to the mobile switchingcenter 300. In this mobile switching center 300, the present inventionis applied, and the same data are synthesized or selected. On the otherhand, in the mobile switching center, a duplication process operation towhich the present invention is applied is carried out for thecommunication data and the control data transmitted from the mobileswitching center 300 to the mobile station 100. The duplicated same datais transmitted via a path of the wire line 250A-the base station 200A-towireless line 150A and another path of the wire line 250B-the basestation 200B-the wireless line 150B to the mobile station 100. Then, theduplicated same data are synthesized, or selected in this mobilestation.

[0041]FIG. 2 schematically shows an arrangement of the mobile switchingcenter 300 in which the present invention is concretely embodied.

[0042] An external BS interface unit 301 stores a plurality of wirelines 250 connected to the base station 200, and executes a data formatconversion, or a frame assembling/desolving operation. For instance, inthe case that a data format in the wire line 250 is an ATM cell, and aformat in a non-instantaneous interrupt handover processing unit 400 isa frame format, this external BS interface unit 301 assembles the framefrom the ATM cell, and vice versa. The non-instantaneous interrupthandover processing unit 400 synthesizes, or selects the same data(frame) of the up stream, which is transferred via the different pathswhen the non-instantaneous interrupt handover is initiated. Also, sincethis non-instantaneous interrupt handover processing unit 400 musttransmit the same data to the different base station, this handoverprocessing unit 400 duplicates data of the down stream. Furthermore, insuch a case that both the communication data and the control data, whichare transferred through the mobile switching station 300, the basestation 200, and the mobile station 100 are transmitted/received withbeing mixed into the same frame, or the same packet, thisnon-instantaneous interrupt processing unit 400 separates andsynthesizes these communication and control data. A switch 302 switcheslines through which data is transferred between the base station sideand the upper-grade network side. Alternatively, this switch 302 may bea packet switch, or an ATM switch. An external upper-grade networkinterface unit 303 stores a line 900 derived from the upper-gradenetwork, and executes a data format conversion, or a frameassembling/desolving operation in a similar manner to the external BSinterface unit 301. A control unit 304 controls various apparatusesinside the mobile switching center 300. The control unit 304 is arrangedby a memory 3006 for saving a program and data, and an MPU 305 foractually controlling the respective apparatuses by executing acalculation process operation. A control signal line 310 is a signalline for transmitting/receiving a control signal containing also thedata among the respective apparatuses within the mobile switching center300.

[0043]FIG. 3 schematically represents an internal arrangement of thenon-instantaneous interrupt handover processing unit.

[0044] Irrelevant to initialization/non-initialization of thenon-instantaneous interrupt handover, the up-stream data frame (will bereferred to as an “upstream frame” hereinafter) received from theexternal BS interface unit 301 is transferred to a framesynchronizing/synthesizing process unit 500. This up-stream frameindicates communication data and/or control data handled as such a framehaving a fixed length or a variable length of a specific length. Also, apacket and an ATM cell will be similarly handled as frames in thefollowing description. When the non-instantaneous interrupt handover isnot initiated, the up-stream frame is transferred to the switch 302without executing any process operations other than the headerconversion. When the communication data is mixed with the control datain this up-stream frame, the communication data is separated from thecontrol data. Thus, the separated control data is transferred to thecontrol unit 304, and the separated communication data fame istransferred to the switch 302. When the non-instantaneous interrupthandover is initiated, a plurality of up-stream frames having the samedata which have been transferred from the different base stations 200are synchronized with each other, and then the synchronized up-streamframes are compared with synthesizing parameters given to these pluralframes, so that only one optimum frame is selected to be transferred tothe switch 302. When the communication data is mixed with the controldata in this up-stream frame, the communication data is separated fromthe control data. Thus, the separated control data is transferred to thecontrol unit 304, and the separated communication data frame istransferred to the switch 302. A synthesizing parameter implies such anindex. That is, error information of a frame in a wireless section, forinstance, an error rate is detected, or measured in unit of theup-stream frame received from the mobile station 100 in the base station200, and this index indicates a quality of this frame obtained from thisdetection, or measurement result, which is received at the base station200. This parameter value is given to each of the frames at the basestation 200, and then is transmitted to the mobile switching center 300.

[0045] The down-stream data frame (will be referred to a “down-streamframe” hereinafter) received from the switch 302 is transferred to aframe multicasting process unit 600. In the case that the mixture of thecommunication data and the control data within the frame is allowed, thecontrol data received from the control unit 304 may be synthesized withthe up-stream frame (arranged by communication data) received from theswitch 302. When the non-instantaneous interrupt handover is notinitiated, the down-stream frame constituted in this manner is processedonly by the header conversion, and then the processed down-stream frameis transferred to the external BS interface unit 301. On the other hand,when the non-instantaneous interrupt handover is initiated, in order totransmit the same data to a plurality of base stations which areconnected to each other by the lines by the same call, the downstreamframe is duplicated to produce only a plurality of down-stream frameswhose number is equal to the plural connections in this framemulticasting process unit 600. Then, only different headers are attachedto the duplicated down-stream frames (so as to transmit data frame todifferent base stations), and a plurality of down-stream framesduplicated at the same timing are transmitted to the external BSinterface unit 301.

[0046] It should be noted that the expression “handover” implies“non-instantaneous interrupt handover” unless a specific instruction isissued.

[0047]FIG. 4 schematically shows an internal arrangement of the framesynchronizing/synthesizing process unit 500.

[0048] A channel number processing unit 510 extracts a channel numbergiven to a received up-stream frame, and transmits this channel numberto a channel/connection management table 520. Then, a connection number,handover information, and a simultaneous connection number, which arereceived from this channel/connection management table 520, are newlyattached to the upstream frame which will then be transmitted to anHO/non-HO frame separating unit 530 (symbol “HO” indicates handover). Achannel number corresponds to the number for specifying a channelthrough which a frame attached with this number is transferred betweenthe base station 200 and the mobile switching center 300. Normally, thisnumber is set every cell. A connection number corresponds to the numberfor specifying a communication between an end and an end, and isexclusively specified every call. During normal communication (namely,handover is not initiated), the channel number corresponds to theconnection number in a one-to-one correspondence. While the handover isinitiated, since the same data is transferred from the base station 200,a plurality of channel numbers are made in correspondence with 1connection number. The correspondence relationship between thisconnection number and the channel number is set by the control unit 304when the handover is initiated. The simultaneous connection number issuch a number indicative of an n-th connection among maximum N pieces ofsimultaneous connections while the handover is initiated, and is savedwith making a one-to-one correspondence with the channel number. Whenthe handover is not initiated, the simultaneous connection number isalways 1. The handover information indicates as to whether or not thehandover process is initiated. If the handover process is initiated,then the handover information includes the maximum simultaneousconnection number “N”. When the handover is not initiated, N is equal to1.

[0049] The channel/connection management table 520 is a table for savinga relationship between the above-described connection numbers andchannel numbers while the call is set and thereafter is released.Furthermore, as to this call, information (handover information) forindicating whether or not the handover is initiated is also saved at thesame time. All of the data managed by this table are written, saved, anddeleted under control of the control unit 304. A detailed structure ofthis channel/connection management table 520 is shown in FIG. 5.

[0050] The HO/non-HO frame separating unit 503 recognizesinitiating/not-initiating of the handover based upon the handoverinformation of the received up-stream frame. When the handover is notinitiated, this frame is transferred to a frame signal multiplexing unit560 without being processed. When the handover is initiated, this frameis transferred to a number/synthesizing parameter analyze processingunit 540.

[0051] In the number/synthesizing parameter analyze processing unit 540the connection number, the frame number, the synthesizing parameter, thesimultaneous connection number, and the handover information (maximumsimultaneous connection number N), which are attached to the frame, areextracted to be transferred to a synthesizing parameter comparisonprocessing unit 550. On the other hand, this frame is transferred to aconnection-depending frame distributing unit. A frame number correspondsto such a number for indicating a sequence of resolved frames when theup-stream data continuously transferred as to the same connection isframed (resolved) in the mobile station 100, the base station 200, orthe external BS interface unit 301. When these frames are assembled toform data and information, these frames are assembled in accordance withthis frame number sequence.

[0052] The synthesizing parameter comparison processing unit 550temporarily saves this information in a synthesizing parameter table 551based on the connection number, the frame number, the synthesizingparameter, the simultaneous connection number, and the handoverinformation (maximum simultaneous connection number N), which arereceived. A detailed structure of this synthesizing parameter table 551is indicated in FIG. 6. In the synthesizing parameter table 551, acomparison of the synthesizing parameter is commenced as to the sameconnection number and the same frame number when such a recognition ismade that all of the synthesizing parameter numbers corresponding to therespective simultaneously connection number have been written. Aselection is made of such a parameter value indicative of the smallesterror rate of the frame from a plurality of synthesizing parameters tobe compared, and a frame having this parameter value is selected fromthe upstream frames having the same data which have been received, andwhose number is equal to the maximum simultaneous connection number N.Then, a decision is made that this selected frame is transmitted to theswitch 302. In a specific connection number and a specific frame number,after the frame to be selected has been determined by theabove-described process operation, a signal (transmission instructionsignal) for instructing either a transmission or a discard every savedframe is transmitted to a same connection correspondence buffer group570 for temporarily saving a plurality of frames having the sameconnection number and the different simultaneous connection numbers.

[0053] The connection-depending frame distributing unit 560 identifies,or discriminates the connection number given to the upper frame, andtransmits this frame to the relevant buffer group of the buffer groupset every connection.

[0054] The same connection correspondence buffer group 570 is such abuffer group to which a plurality of buffers are allocated incorrespondence with the different simultaneous connection number withrespect to each of connections while the handover is initiated, the sameconnection correspondence buffer group 570 identifies, or discriminatesthe same connection number attached to the received frame, and storesthis frame into a buffer corresponding to the above-explainedsimultaneous connection number among a plurality of buffers temporarilyprovided with respect to each of the simultaneous connection numbers. Inresponse to the transmission instruction signal issued from thesynthesizing parameter comparison processing unit 550, as to the pluralframes having the same connection number and the different simultaneousconnection numbers stored in this buffer group, the respective framesare transmitted and discarded. The transmission instruction signalinstructs only a frame having a specific simultaneous connection numberamong a plurality of frames having the specific connection numbers, thespecific frame numbers, and the different simultaneous connectionnumbers to be transmitted to the frame signal multiplexing unit 580, andalso instructs the remaining frames having the same connection numbersto be discarded.

[0055] The frame signal multiplexing unit 580 multiplexes the non-HOframe received from the HO/non-HO frame separating unit 530, and the HOframe received from the same connection correspondence buffer group, andthen transmits the multiplexed frames to a signal separating unit 590.

[0056] In the case that the received frame corresponds to such a framethat the communication data is mixed with the control data, the signalseparating unit 590 extracts only the control data, and transmits thiscontrol data via the control signal line 310 to the control unit 304. Onthe other hand, the remaining communication data is transmitted as aframe to the switch 302 in combination with the header information.

[0057]FIG. 5 shows a data save structure of the connection/channelmanagement table 520.

[0058] The data items saved in the connection/channel management table520 are a connection number 521, a channel number 525, a simultaneousconnection number 526, and non-instantaneous interrupt handover ON/OFF523 and a maximum simultaneous connection number 524 as handoverinformation 522. The information other than the instantaneous connectionnumber 526 corresponds to information transferred from the control unit304 when the call is set and the handover is initiated, and is deletedin response to the instruction from the control unit 304. Thesimultaneous connection number 526 is set from the maximum simultaneousconnection number 524. For instance, when the maximum simultaneousconnection number is 2, “1” and “2” are set as the simultaneousconnection number 526.

[0059]FIG. 6 shows a data save structure of the synthesizing parametertable 551.

[0060] The data items saved in the synthesizing/parameter table 551 area connection number 552, a maximum simultaneous connection number 553, aframe 554, a simultaneous connection number 555, and a synthesizingparameter 556. All of the above-described information is transferredfrom the synthesizing parameter comparison processing unit 550 to besaved. As to a specific connection number and a specific frame number,at the time when all of the synthesizing parameter values are saved, thesynthesizing parameter value is read from the synthesizing parametercomparison processing unit 550, and then the item portion of the framenumber 554, the item portion of the simultaneous connection number 555,and the item portion of the synthesizing parameter 556 related to thesynthesizing parameter to be read are deleted. A series of these processoperations is carried out in correspondence with the connection numberand the frame number.

[0061]FIG. 7 represents a sequential operation of a frame transferoperation and a control signal transfer operation as to a specificup-stream frame of a specific call within the framesynchronizing/synthesizing process unit 500.

[0062] At the same time when the call is set, the control unit 304transfers the channel number and the connection number related to thiscall to the channel/connection management table 520 (701). Also, whenthe handover is initiated, the handover information is transferred via asimilar path. These information transmitted from the control unit 304 istemporarily saved in the channel/connection management table 520.

[0063] The channel number analyze processing unit 510 receives anup-stream frame 1 (702) constructed of the communication data, thecontrol data, and the header information (containing channel number andframe number) from the external BS interface unit 301. This channelnumber analyze processing unit 510 extracts the channel number from thisup-stream frame 1 (702) and transmits this channel number to thechannel/connection management table 520 (711).

[0064] In the channel/connection management table 520, the connectionnumber, the handover information, and the simultaneous connection numberare read to be transmitted to the channel number analyze processing unit(712).

[0065] In the channel number analyze processing unit 510, the connectionnumber, the handover information, and the simultaneous connectionnumber, which are received, are attached to the up-stream frame 1 (702)as new header information, and then an up-stream frame 2 (713) istransmitted to the frame distributing unit 530.

[0066] The frame distributing unit 530 identifies whether or not theup-stream frame corresponds to a frame under initiation of the handoverbased on the header information (handover information) of the upstream 2(713). When this frame is identified as the frame under initiation ofthe handover, a frame 3 (713) is transmitted to the number/synthesizingparameter analyze processing unit 540. When the handover is not yetinitiated, an up-stream frame 9 (732) is transmitted to a frame signalmultiplexing unit 580.

[0067] The number/synthesizing parameter analyze processing unit 540extracts from the header information of the up-stream frame 3 (731), theconnection number, the frame number, the simultaneous connection number,the maximum simultaneous connection number, and the synthesizingparameter value, and then transmits these extracted information to thesynthesizing parameter comparison processing unit 550 (742). Theup-stream frame 3 (731) is transmitted as an up-stream frame 4 (741)having a similar format to the connection-dependent frame distributingunit 560.

[0068] In the synthesizing parameter comparison processing unit 550,synthesized information received from the number/synthesizing parameteranalyze processing unit 540 is temporarily saved in the synthesizingparameter table 551. In the synthesizing parameter table 551, when allof the synthesizing parameters whose number is equal to the maximumsimultaneous connection number related to a single handover are receivedand saved, a plurality of these synthesizing parameter values are read.Such a value for indicating the frame having the smallest error rate isselected, and a decision is made that only an up-stream frame having thesimultaneous connection number related to this parameter value isselected and transmitted. As to the up-stream frames related to othersimultaneous connection numbers, a decision is made that these up-streamframes are discarded. After the transmission and the discard aredetermined, a transmission allow/not allow signal 751 for instructingthe frame transmission or the frame discard is transmitted to therespective buffers of the relevant connection in the sameconnection-depending buffer group 570.

[0069] In the connection-depending frame distributing unit 560, anup-stream 5 (761) similar to the up-stream frame 4 (741) is transmittedfrom the header information (connection information) of the receivedup-stream frame 4 (741) to the relevant same connection-depending buffergroup 570.

[0070] The same connection-depending buffer group 570 owns buffers whosenumber is equal to the maximum simultaneous connection number every sameconnection, and stores the frame 5 (761) into the corresponding bufferfrom the simultaneous connection number equal to the header informationof the up-stream frame 5 (761). Then, in the case that a transmissionallow-not allow signal 751 a for instructing the frame transmission isreceived from the synthesizing parameter comparison processing unit 550,an up-stream frame 6 (771) similar to the up-stream frame 5 (761) istransmitted to the frame signal multiplexing unit 580. On the otherhand, when transmission allow/not allow signals 751 b and 751 c forinstructing frame discards are received from the synthesizing parametercomparison processing unit 550, the frame discarding process operationsare carried out in the respective buffers.

[0071] The frame signal multiplexing unit 580 multiplexes the up-streamframe 6 (771) received from the same connection-depending buffer group570, and the upstream frame 9 (731) received from the frame distributingunit 530 as a frame 7 (781) having a similar format, and thereaftertransmits this processed frame 7 to the signal separating unit 590.

[0072] When the received up-stream frame 7 (781) is such a frame made bymixing the communication data with the control data, the signalseparating unit 590 extracts the control data and transmits thisextracted control data as a control signal 792 to the control unit 304.A frame constructed of the communication data and the header informationis transmitted as an up-stream 8 (791) to the switch 302.

[0073]FIG. 8 shows an internal arrangement of the frame multicastingprocess unit 600.

[0074] A signal synthesizing unit 610 synthesizes control data forcontrolling the mobile station 100, which is received from the controlunit 304, with respect to such a down-stream data frame (will bereferred to as a “down-stream frame” hereinafter) which contains onlythe communication data except for the header and received from theswitch 302. The downstream frame transmitted from the signalsynthesizing unit 610 may allow that the communication data is mixedwith the control data due to this synthesization. After thissynthesization, this shown-stream frame is transmitted to a frame numberapplying unit 620.

[0075] The frame number applying unit 620 recognizes and extracts theconnection number applied to the header of the received down-streamframe, and then transmits the extracted connection number to a framenumber counter 630. Thereafter, a frame number returned from the framenumber counter 630 is newly applied to this frame, and the resultingframe is transmitted to a connection number analyzing unit 640.

[0076] In the frame number counter 630, a sequential number counter isheld every connection number. This counter is held when the call settingoperation is commenced until the call is released. The frame numbercounter 630 identifies the connection number received from the framenumber applying unit 620, reads out the present counter value of thisidentified connection number, and then returns this present countervalue to the frame number applying unit 620. At the same time, the countvalue is counted up.

[0077] A connection number analyzing unit 640 identifies and extractsthe connection number of the downstream frame received from the framenumber applying unit 620, and transmits the extracted connection numberto a channel/connection management table 650. Thereafter, the connectionnumber analyzing unit 640 receives the handover information and thechannel number from this management table 650. The information relatedto these down-stream frame is transmitted to a frame signal duplicationprocessing unit 660 irrelevant to the downstream frame. When thehandover is initiated, the above-described channel number becomesplural. On the other hand, the down-stream frame is transmitted to theframe signal duplication processing unit 660 without being specificallyprocessed.

[0078] The channel/connection management table 650 is similar to thechannel/connection management table 520 provided inside the framesynchronizing/synthesizing process unit 500. Alternatively, both thechannel/connection management tables 520 and 650 may be made as a singletable which is commonly used in the frame synchronizing/synthesizingprocess unit 500 and the frame multicasting process unit 600.

[0079] The frame signal duplication processing unit 660 receives thedown-stream frame and also various information (handover information andchannel number) related to this down-stream frame from the connectionnumber analyzing unit 640. In the case that the frame signal duplicationprocessing unit 660 recognizes that a call related to this frame isunder initiation of the handover based on this down-stream frame, thisframe signal duplication processing unit 660 duplicates down-streamframes whose number is equal to the maximum simultaneous connectionnumber corresponding to a portion of the handover information. Since thedifferent channel numbers which have already been received are newlyapplied to the duplicated down-stream frames, the multicasted basestations are specified. Furthermore, the duplicated frames aretransmitted to the corresponding connection-depending buffer group 670based on the applied connection numbers (since all of connection numbersof duplicated frames have the same values, these duplicated frames aretransmitted to the same buffer group). On the other hand, when thehandover is not initiated, no frame duplication is carried out. However,the channel number is newly applied to the received frame, and theresulting frame is transmitted to the corresponding connection-dependingbuffer group 670.

[0080] The connection-depending buffer group 670 is similar to theconnection-depending buffer group 570 provided in the framesynchronizing/synthesizing process unit 500, and the process operationof which is similar to that of the frame synchronizing/synthesizingprocess operation. It should be noted that all of timing control signalsreceived from a timing control processing unit 680 are such signals forinstructing transmissions. Upon receipt of this timing control signal,the down-stream frames of the same frame numbers are transmitted fromthe respective buffers related to the same connection, so that themulticasting operation is performed at this timing. Also, when thehandover is not yet initiated, the timing control signal is received ina similar manner, and the down-stream frame is transmitted.

[0081] When a call is set and/or a communication is established, thetiming control processing unit 680 receives frame transmission timinginformation related to this call from the control unit 304, andtransmits a timing control signal based upon this frame transmissiontiming information to the same connection-depending buffer group 670.

[0082] The frame signal multiplexing unit 690 multiplexes a plurality ofdown-stream frames received from the same connection-depending buffergroup 670, and then transmits the multiplexed down-stream frame to theexternal BS interface unit 301.

[0083]FIG. 9 represents a frame transfer operation related to a specificdown-stream frame of a specific call, and also a control signal transfersequence within the frame multicasting process operation.

[0084] The signal synthesizing unit 610 synthesizes a down-stream frame1 (801) received from the switch 302 with a control signal 802 receivedfrom the control unit 304, and then transmits the synthesized frame as adown-stream 2 (812) to the frame number applying unit 620. Thedown-stream frame 1 (801) is constructed of the communication data andthe header information (connection number is contained). The controlsignal 802 is arranged by control data used to control the mobilestation 100 from mobile switching center 300.

[0085] The frame number applying unit 620 extracts the connection numberfrom the header information of the down-stream frame 2 (812) receivedfrom the signal synthesizing unit 610, and transmits the extractedconnection number to the frame number counter unit 630 (821).Thereafter, a frame number 822 returned from the frame number counterunit 630 is added as new header information of this down-stream frame 2(812), and the added frame is transmitted as a down-stream frame 3 (823)to the connection number analyzing unit 640.

[0086] The frame number counter unit 630 judges whether or not thedown-stream frame corresponds to any counter provided every connectionbased upon the received connection number, reads out a counter value ofthe corresponding counter, and then returns the read counter value tothe frame number applying unit 620. After the counter value is read out,this counter value is counted up.

[0087] The connection number analyzing unit 640 extracts the connectionnumber from the header information of the down-stream frame 3 (823)received from the frame number applying unit 620, and then transmits theextracted connection number to the channel/connection management table650. Thereafter, in response to the connection number 842, the handoverinformation, channel number, and simultaneous connection number arereceived (851), and each of the above-described information istransmitted to the frame signal duplication processing unit 660 (843).On the other hand, the down-stream frame 3 (823) is transmitted as aframe 4 (841) having a similar format to the frame signal duplicationprocessing unit 660.

[0088] The channel/connection management table 650 owns a similaroperation to that of the channel/connection management table 520employed in the frame synchronizing/synthesizing process unit 500.

[0089] As the down-stream frame 4 (841) and information (843) related tothis down-stream frame, the frame signal duplication processing unit 660receives handover information, a channel number, and a simultaneousconnection number. When such a fact that the handover is initiated isidentified from the handover information, the frame signal duplicationprocessing unit 660 duplicates the down-stream frames 4 (841) whosenumber is equal the maximum simultaneous connection number contained inthis handover information. To the duplicated down-stream frames 4 (841),channel numbers and simultaneous connection numbers are newly added asheader information. These channel numbers specify the base stations andthe channels for the transmission destination. After these processoperations are executed, down-stream frames 5 (861) are transmitted tothe respective buffers of the corresponding same connection numberbuffer group 670 from the connection number and the simultaneousconnection number, which are equal tot he header information of thedown-stream frames 5 (861) duplicated from the down-stream frames 4(841). When the handover is not yet initiated, the frames are notduplicated. However, similar frames 5 (861) are transmitted to the sameconnection number buffer group 670. On the other hand, after theabove-explained down-stream 5 (861) has been transmitted, a transmissioncompletion signal 862 is transmitted to the timing control unit 680.Accordingly, such a fact that the transmission of the down-stream frames5 (861) is completed is transferred. It should be understood that thetransmission completion signal 862 also contains the connection number,the maximum simultaneous connection number, and the frame number.

[0090] Upon receipt of the transmission completion signal 862, thetiming control processing unit 680 transfers by using a transmissioninstruction signal 881, such a fact that all of the down-stream frames 5(861) having the frame numbers corresponding to the down-stream frames 5(861) stored in the respective buffers of a specific sameconnection-depending buffer group 670 are transmitted based upon aconnection number, a maximum simultaneous connection number, and a framenumber of internal information of this transmission completion signal862. The timing at which the transmission instruction signal 881 can betransmitted is notified from the control unit 304 when the call is set,or when the handover is initiated, and the transmission instructionsignal 881 s transmitted at this timing information.

[0091] When the transmission instruction signal 881 is received from thetiming control processing unit 680, each of the buffers which havestored the down-stream frames 5 (861) of the same connection-dependingbuffer group 670 transmits the down-stream frame 5 (861) having therelevant frame number to the frame signal multiplexing unit 690 as adown-stream frame 6 based upon a frame number equal to the internalinformation of this transmission instruction signal 881.

[0092] The frame signal multiplexing unit 690 multiplexes thedown-stream frames 6 (871) transmitted from the sameconnection-depending buffer group 670 as a down-stream frame 7 (891),and transmits the multiplexed down-stream frame 7 (891) to the externalBS interface unit 301.

[0093]FIG. 10 schematically indicates a control signaltransmission/reception sequence when soft handover is initiated in amobile communication network system to which the present invention isapplied.

[0094] While a communication (161, 261) is executed among the mobilestation 100, a base station A200A, and the mobile switching center 300,this mobile station 100 initiates the soft handover. First, the mobilestation 100 transmits to the base station A200A, a handover connectionrequest message (162) containing information for identifying a newlycommunicatable base station B200B. Similar to the mobile station, thisbase station A200A transmits a handover connection request message 262to the mobile switching center.

[0095] The mobile switching center 300 which has received this handoverconnection request message analyzes the information for identifying thenewly communicatable base station B200B contained in this message, andthen transmits another handover connection request message 263 to thisbase station 200B. The base station 200B which have received thishandover connection request message 263 judges as to whether or not aresource of a wireless section can be allocated, for instance, awireless channel and a hard resource employed in this base station canbe allocated. When the base station B200B judges that the resource canbe allocated, this base station B200B transmits a handover connectionrequest Ack 264 containing the allocated wireless channel information tothe mobile switching counter 300. The mobile switching center 300 whichhas received this message connection request Ack 264 allocates a channelbetween the base station 200 and the mobile switching center 300, andthen causes a channel number of this allocated channel to be stored intothe channel/connection management table 520 shown in FIG. 6 in relationto a connection number. Also, the mobile switching center 300 setsnon-instantaneous interrupt handover On/Off information 523corresponding to one of the handover information 522 contained in thismanagement table 520 from “Off” to “On”, and changes the maximumsimultaneous connection number 524 from “1” to “2”, so that thesimultaneous connection number 526 related to the newly added channelnumber is set to “2”.

[0096] After the setting operation of the channel/connection managementtable 520 has been completed, the mobile switching center 300 transmitsa handover connection request Ack message 265 to the base station A200A.The base station A200A which has received this message 265 will transmita handover connection request Ack message 163 to the mobile station 100.The mobile station 100 which has received this request message willrecognize that soft handover with the base station B200B is available,and commences the communications at the same time with respect to thebase station A200A and the base station B200B.

[0097] Both the base stations A and B communicate with the mobileswitching center 300, and the mobile switching center 300 causes theup-stream frames received from the respective base stations to beframe-synthesized in the frame synchronizing/synthesizing unit 500.Also, the down-stream frames transmitted to the respective base stationsare duplicated and transmitted in order that the duplicated down-streamframes can be transmitted to the respective base stations in the framemulticasting process unit 600 shown in FIG. 8.

[0098] When the line quality with respect to the base station A200A islowered, the mobile terminal 100 transmits handover cut request messages165A and 165B containing the information for identifying the basestation B200B so as to request that the line connected to the basestation A200A is cut. Similarly, both the base stations 200A and 200Bwhich have received this handover cut request messages 165A and 165Bwill transmit handover cut request messages 267A and 267B to the mobileswitching center 300. In the mobile switching center 300, these handovercut request messages 267A and 267B are synthesized to produce a singlemessage in the frame synchronizing/synthesizing processing unit 500.Thereafter, this single message is analyzed, and a handover cut requestmessage 268 is transmitted together with information for identifying thebase station 200A, which is contained in this single message, to thebase station A200A. The base station A200A which has received thismessage 268 accomplishes the communication with the mobile station 100,and then transmits a handover cut request Ack message 269 to the mobileswitching center 300 in order to notify the completion of thiscommunication. Similarly, the mobile switching center 200 transmits thehandover cut request Ack message to the base station B200B, and thisbase station B200B transmits this message to the mobile station 100.Then, this mobile station 100 recognizes that the handover is ended, andcontinues the communication only with the base station B200B (167).

[0099]FIG. 11 indicates a sequence defined when the mobile station 100issues a call, and then a connection and a channel is set to therebyestablish a communication.

[0100] The mobile station 100 transmits connection establish requestmessage 151 and 251 via the base station 200 to the mobile switchingcenter 300 when the call is issued. The mobile switching station 300which has received this connection establish request message 251recognizes that the mobile station 100 requests to issue a call, and atthe same time, sets the connection with this mobile station 100. Also,this mobile switching center 300 allocates a channel in order tocommunicate with the base station 200. A connection/channel relationshipwhen the connection is set and the channel is allocated is written intothe channel/connection management table 520 shown in FIG. 5, and is helduntil this connection is released (292).

[0101] The mobile switching center 300 when the connection and thechannel have been set transmits a connection establish notify message252 containing these connection number and channel number to the basestation 200. Then, the base station 200 recognizes such a channel thatthe communication is subsequently carried out based on the channelnumber contained in this message 252. Thereafter, the base station 200transmits a connection establish notify message 153 containing theconnection number to the mobile station 100. Since the mobile station100 receives this notify message 153, this mobile station 100 recognizesthat the connection between this mobile station 100 and the mobileswitching station 300 can be established, and at the same time, holdsthis connection number until the connection is released.

[0102] After the connection has been established between the mobileterminal 100 and the mobile switching center 300, a call is set (253)and thus a telephone communication is commenced (254).

[0103]FIG. 12 represents a structure of a frame transmitted/receivedbetween the mobile terminal 100 and the non-instantaneous interrupthandover processing unit 400 employed in the mobile switching station300.

[0104] An up-stream line frame is arranged by user information 101 onwhich voice and user specific information are mounted when beingtransmitted from the mobile terminal 100, control information 792 usedto control the line with the mobile switching center 300, and a framenumber 554 used to specify a sequence of frames to be transmitted. Inthe base station 200 which has received this frame, error information inthe wireless section of this up-stream line frame when being received isproduced, and then this error information is applied to this frame as asynthesizing parameter 556. Also, a specific channel number 525allocated so as to transmit this up-stream line frame to the mobileswitching station 300 is also attached. The frame produced by theabove-explained process operation is received by the non-instantaneousinterrupt handover processing unit 400 of the mobile wireless station300. Further, the connection number 521, the handover information 522,and the simultaneous connection number 526 are applied to this receivedframe by executing the process operations shown in FIG. 4 and FIG. 7 inthe frame synthesizing/synthesizing process unit 500 equal to theinternal process unit.

[0105] When a down-stream line frame is received by thenon-instantaneous interrupt handover processing unit, this down-streamline frame is constructed of the user information 101 and the controlinformation 792. Since this down-stream line frame is processed by theprocess operations as described in FIG. 10 and FIG. 11, the connectionnumber 521, the frame number 554, and the channel number 525 areattached, and thereafter the resulting frame is transmitted to the basestation 200. The base station 200 which has received this down-streamline frame transmits such a frame from which the channel number 525corresponding to the information irrelevant to the mobile station 100has been deleted to the mobile station 100.

[0106] As previously described in detail, according to the presentinvention, in the mobile communication network in which theATM-processed transfer paths are present between the mobile stations andthe mobile switching center, even when each of the frames (containingATM cell, short cell, and packet) involving the data sent from themobile stations is received in the asynchronous manner, the connectioncan be specified from the header information related to this frame, andthe information saved in the mobile switching center. Also, it ispossible to identify in unit of the frame as to whether or not thehandover is initiated in this connection. As a consequence, the pluralframes containing the same data during the non-instantaneous interrupthandover can be compared and selected, which could be conventionallyrealized only in the STM system. Also, since the frames containing theduplicated data which should be transmitted from the mobile switchingcenter to the mobile terminal are simultaneously transmitted at thespecific timing, the frames can be easily selected and synthesized ineither the base station on the reception side or the mobile stations ina similar manner to the STM system. Furthermore, the non-instantaneousinterrupt handover which could be realized only in the STM system canalso be realized in the ATM system.

1. A switching center connected to a plurality of base stations, aplurality of said base stations communicated with a plurality ofwireless stations, said switching center comprising: a initiating unitwhich initiates a handover process operation in order that while any ofsaid wireless stations is connected to a first base station, said anywireless station should be newly connected to a second base stationirrelevant to said first base station; a receiver unit receives a firstpacket, which is converted information from said wireless station intoby said first base station, transmitted by said first base station and asecond packet, which is converted information from said wireless stationinto by said second base station, transmitted by said second basestation; a buffer unit which temporarily stores said first packet andsaid second packet, which are received at asynchronous timing, so as tobe synchronized with each other; a calculating unit which calculateserror rates of said first and second packets synchronized with eachother; a selecting unit which selects such an packet whose error rate islower than that of the other packet; and a cutting out unit which cutsout the connection between said wireless station and said first basestation when such a condition that the error rate of said second packetexceeds the error rate of said first packet becomes a normal condition.2. A switching center as claimed in claim 1 , further comprising: adiscarding unit which discards the packet having the worse error rate.3. An information processing station connected to a plurality of basestations communicated with a mobile wireless station, for processingcommunication information transmitted from said base stations,comprising: a receiver unit which receives asynchronous frames which aresuperimposed information respectively derived from the same mobilewireless station and then are transferred by said plurality of basestations; a buffer unit which temporarily stores said asynchronousframes received in the asynchronous timing so as to be synchronized witheach other; and a selector unit which selects an asynchronous framehaving a better condition from said asynchronous frames stored by saidbuffer unit.
 4. A switching center as claimed in claim 3 , wherein saidselector unit selects an asynchronous frame having a better conditionfrom said asynchronous frames having the same transmission order hasbeen added by said mobile wireless station.
 5. A mobile communicationsystem as claimed in claim 4 , wherein said transmission ordercorresponds to a connection number specifically determined every time asingle communication is established.
 6. A mobile communication system asclaimed in claim 4 , further comprising: a judging unit which judgesinformation for indicating whether or not the handover process operationis under initiation, which is added to said frame by said mobilestation; wherein said buffer unit stores the asynchronous framestransferred from the same mobile station via said plurality of basestations when said judgement result indicates that the handover processoperation is under execution, and said selector unit selects such anasynchronous frame having a better condition, and outputs the selectedasynchronous frame, whereas when said judgement result indicates thatthe handover process operation is not under execution, said informationprocessing station directly outputs the received asynchronous frame. 7.A switching center for executing a handover processing method for aplurality of base stations communicated with a mobile wireless station,said switching center comprising; a recognizing unit which recognizeswhich connection between two among said stations a frame containing datato be transmitted to the mobile wireless terminals belongs to; aapplying unit which applies such a number indicative of the same frametransmission order to a frame which is judged as the same connection bysaid recognizing unit; a duplicating unit which duplicates the frame towhich the frame transmission order number has been applied to obtain aplurality of such frames whose number is equal to a total number of saidbase stations which execute the handover process operation; and asynchronizing unit which synchronizes the duplicated frames with eachother and transmitting the synchronized duplicated frames.